The present invention relates to apparatus and methods for effecting ultrasonic bonding on at least one continuously moving web or work piece attached to a continuously moving web using ultrasonic bonding apparatus. The invention more particularly concerns apparatus and methods for ultrasonically bonding at least one continuously moving web using a rotary ultrasonic horn.
It is known to bond at least one continuously moving substrate web by constrictively passing the web between a rotating ultrasonic horn and a rotating anvil roll. Typically, the anvil roll includes one or more arrays of raised projections configured to bond the web in a predetermined bond pattern. The rotary ultrasonic horn is capable of expressing ultrasonic energy at a bonding surface to ultrasonically bond the web as the web constrictively travels between the rotary ultrasonic horn and the anvil roll. Representative examples of rotary ultrasonic horns which have been used to bond at least one web are described in U.S. Pat. No. 5,096,532 to Neuwirth et al issued Mar. 17, 1992; and U.S. Pat. No. 5,110,403 to Ehlert issued May 5, 1992.
The consistency and quality of the bond when using such rotary bonding techniques is dependent on the consistency of the force exerted on the web by the combination of the anvil roll and the bonding roll; the time during which the web is being pressed in the constrictive nip which is dependent on the operating speed; and the types of materials being bonded. The consistency and quality of the bonds are also dependent on the frequency and amplitude of the vibrations of the ultrasonic horn, and the percent bond area which is the area of the pins (projections) in the bond region divided by the surface area of the bond region.
Conventional methods for rotary bonding include a rotating ultrasonic horn which is mounted in a cantilevered configuration such that the horn is not supported about the surface of the bonding roll. However, such conventional methods have not always been sufficiently satisfactory.
The inventors herein have discovered that, while a variety of factors can be adjusted and controlled in defining a more uniform bonding pattern, stiffness/rigidity of the entirety of the bonding apparatus is a critical factor in achieving desired bond uniformity.
Use of a cantilevered bonding roll has inherent limitations which adversely affect the bond quality and which in this invention can be at least partially corrected by replacing the cantilever configuration with an in-line or balanced force application which avoids application of forces through cantilevered configurations. In cantilevered configurations, it has been very difficult to maintain the desired degree of consistency and stability of nip force between the bonding roll and the anvil roll. As a result, in many conventional methods for rotary bonding, bond quality and/or consistency has been undesirably variable both along the length of the bond region and across the width of the bond region. In addition, processes using cantilevered rotary ultrasonic horns have not been as robust as desired for a manufacturing environment.
Consistency and quality of bonds when using conventional rotary ultrasonic bonding methods and apparatus has been particularly variable where the desired bond pattern is intermittent because the nip pressures inherently change in concert with the intermittent nature of the bonding operation.
When using conventional methods for rotary bonding in such configuration, the bond quality has typically been less than satisfactory along the length of the bond pattern. Such inconsistency in the bond pattern has been due, at least in part, to inconsistent levels of force being effectively applied along the length of respective intermittent bond regions of the bond pattern. Typical of such inconsistency is excessive nip loading at the leading edge of the bond region, and insufficient nip loading behind the leading edge of the respective element as the bonding apparatus flexes or deflects in combination with development of the respective bonding region at the nip. Both the excessive nip loading and the insufficient nip loading have resulted in poor bond quality and poor bond consistency.
Under excessive loading, so much energy may be applied to the materials being bonded as to burn through or otherwise excessively soften the materials being bonded, as well as to apply excessive pressure to the softened materials, whereby bonds so formed may be weak, and/or may be uncomfortably harsh to the touch of a wearer""s skin. In the alternative, excessive loading can physically damage, as by tearing, the material being bonded. Additionally, excessive loading can increase wear and thus damage the ultrasonic horn. Finally, ultrasonic horns are generally driven by piezoelectric crystals that convert electrical energy at high frequency into mechanical vibrations. When an excessive impulse load is applied to the horn, the process works in reverse and the resulting electrical spike can overload and shut down the electrical frequency generator.
Generating ultrasonic bonds depends on the combination of frequency and amplitude of the vibrations, the amount of pressure applied, and the time during which pressure is applied. Under conditions of insufficient loading at the nip, too little pressure is applied to the materials to be softened thereby, whereby the amount of energy transferred to the elements to be bonded together is insufficient to develop sufficiently strong bonds.
Conventional methods for rotary bonding have used different approaches to diminish the variations in consistency of the interference. For example, the bonding roll, anvil roll, and support frames have been precisely machined to minimize runout in the bonding system.
As used herein, the term xe2x80x9crunoutxe2x80x9d expresses changes in the radius of the anvil roll and/or the rotary ultrasonic horn about the circumference of the respective rotary element.
The above-mentioned difficulties of maintaining desired bond quality and consistency along both the length and width of the web become even more acute when intermittently bonding at least one continuously moving web using a rotary ultrasonic horn. Operation of a rotary ultrasonic horn includes movement inherent in the continuous vibration of the horn at a given frequency and amplitude to efficiently bond the web. as well as rotation of the horn along the length of a web which may vary in thickness along the length of the web, thus to impose varying resistance to the nip pressure applied by the combination of the horn and the anvil on the web. Under certain conditions, such vibratory movement of the horn, and variation of web thickness, either alone or in combination, may adversely affect bond consistency and quality in the web.
For example, because the ultrasonic horn must vibrate at its resonant frequency like a bell. the shaft supporting the horn cannot be rigidly mounted e.g. to a frame. The need to provide non-rigid mounts for e.g. non-rigid mounting corresponds with a tendency for the horn to be deflected from a desired position under the nip forces required to achieve bonding using ultrasonic energy to develop the desired bonds or to be deflected, under its own dead weight. Typically, the rotary ultrasonic horn has conventionally been mounted in a cantilevered configuration which enhances the amount by which the position of the horn is changed when going from a dead-weight self-supporting mass being acted on by gravity to a fully loaded bond nip.
For example, a horn assembled in a conventional and typical mount extends from a generally horizontal shaft. The shaft rests on rubber O-rings. When the horn is so mounted in a generally horizontal orientation, with the O-rings taking the load, the axis of the horn sags out of true alignment with the shaft support structure which supports the shaft, the horn, and optionally the drive mechanism. Such sag is typically about 0.015 inch at the horn face for a 20 pound horn.
In addition, where the web advancing through the nip, defined between the horn and the anvil, varies in thickness and/or density the web applies a correspondingly varying back pressure on the horn and anvil. The overall result of nip variation, then, can be defined in terms of the combination of the degree of variability in manufacturing and mounting the horn and anvil, as well as the degree of variability in thickness of the web moving through the nip between the anvil and horn.
These difficulties are even further exacerbated when the rotary ultrasonic bonding includes an intermittent bond pattern as discussed above such that a discrete raised array of bonding projections is introduced into the nip at the initiation of bonding of each bond region.
It is an object of this invention to provide bonding apparatus and methods wherein nip pressure is more consistent along the lengths and widths of respective bonding regions.
It is a more specific object to provide rigid and stiff bonding apparatus wherein reduced interference can be employed while achieving an effective level of nip loading at the bonding nip.
It is a further object to provide a method for developing bond consistency between bond regions while attenuating pressure and bond variation internal to the respective bond regions.
The invention is defined in a first family of embodiments comprehending ultrasonic bonding apparatus for intermittently creating ultrasonic bonds in sequentially advancing work piece segments. in a nip. The work piece segments to be bonded are up to about 0.25 inch thick. The ultrasonic bonding apparatus comprises a frame. Anvil support apparatus defines an anvil loading assembly connected to the frame, and supporting an anvil roll mounted for rotation about a first generally horizontal axis. The anvil roll comprises a first relatively smaller radius portion extending about a first portion of a circumference of the anvil roll, and at least one raised bonding portion having a second relatively larger radius extending about a second portion of the circumference of the anvil roll. Horn support apparatus is connected to the frame, and supports a rotary ultrasonic horn mounted for rotation about a second generally horizontal axis, and aligned with the first generally horizontal axis. The ultrasonic horn and the anvil roll are collectively mounted and configured such that the ultrasonic horn and the anvil roll can be brought together to define a nip therebetween, and wherein the anvil roll and the ultrasonic horn can rotate in common with movement of work piece elements through the nip, and intermittent passage of the raised bonding portion through the nip. The frame, the anvil support apparatus, and the horn support apparatus collectively are sufficiently rigid that the horn and the anvil roll can be brought together with interference levels of from about 0.000 inch to about 0.008 inch at the raised bonding portion in combination with defining sufficient nip pressure to develop ultrasonic bonds in the work piece segments passing through the nip.
In some embodiments, a width is defined between the ultrasonic horn and the anvil roll, and the anvil support apparatus includes a resilient support member defining a resistance, to withdrawal of the anvil roll from the nip, of about 400 pounds per inch width of the nip.
In some embodiments, the anvil support apparatus further comprises a lifting plate for lifting and lowering the anvil loading assembly with respect to the ultrasonic horn.
In some embodiments, the anvil support apparatus further comprises a pivot plate pivoting the anvil loading assembly about a third axis oriented perpendicular to the first axis.
Some embodiments can include a stop defining a limit to downward travel of the anvil loading assembly.
Preferred embodiments include a back-up roll mounted above the ultrasonic horn, and wherein the back-up roll engages an outer surface of the ultrasonic horn in alignment with the first and second axes.
Preferred embodiments include an adjusting screw, operating on a cradle arm, for adjusting a height of the back-up roll, and thus generally defining an upper limit to movement of the ultrasonic horn.
Preferred embodiments can include first and second support rolls releasably supporting opposing sides of an outer surface of the ultrasonic horn.
Preferably, the first and second support rolls are positioned lower than the axis of the ultrasonic horn, whereby urging the first and second support rolls inwardly against the outer surface of the ultrasonic horn lifts the ultrasonic horn upwardly against the back-up roll.
Preferably, the first and second support rolls are mounted to a horn support plate through an activation assembly, the horn support apparatus further comprising equalizer arms mounted to the horn support plate, and equalizing inward and outward movement of the first and second support rolls.
In a second family of embodiments, the invention comprehends a method of intermittently creating ultrasonic bonds in sequentially advancing work piece segments, wherein the work piece segments to be bonded are up to about 0.25 inch thick. The method comprises passing the work piece segments through a nip defined by a frame, anvil support apparatus, and horn support apparatus. The anvil support apparatus defines an anvil loading assembly connected to the frame and supporting an anvil roll mounted for rotation about a first generally horizontal axis. The anvil roll comprises a first relatively smaller radius portion extending about a first portion of a circumference of the anvil roll and at least one raised bonding portion having a second relatively larger radius extending about a second portion of the circumference of the anvil roll. The horn support apparatus is connected to the frame, and supports a rotary ultrasonic horn mounted for rotation about a second generally horizontal axis, the second axis being aligned with the first axis. The method further comprises bringing the ultrasonic horn and the anvil roll together in defining the nip, with interference of about 0.000 inch to about 0.008 inch at the raised bonding portion, and correspondingly developing suitable pressure in the nip to create ultrasonic bonds. In some embodiments, in the case where interference is substantially 0.000 inch, the combination of work piece segment(s) in the nip and amplitude of the horn face when vibrating generate the desired nip pressure. The method includes activating ultrasonic energy in the ultrasonic bonding horn, and rotating the ultrasonic horn and anvil roll in common with movement of the work piece segments through the nip, and thereby intermittently applying pressure to the work piece segments at the raised bonding portion, and creating ultrasonic bonds in the work piece segments passing through the nip.
The method can include applying first and second support rolls to sides of the ultrasonic horn and lifting the ultrasonic horn into engagement with a back-up roll aligned with the first and second axes such that the first and second support rolls, in combination with the back-up roll, define a fixed location of the ultrasonic horn.
The method can also include applying the first and second support rolls to the sides of the ultrasonic horn at locations lower than the second axis, and urging the first and second support rolls against the ultrasonic horn and thereby lifting the ultrasonic horn into engaging relationship with the back-up roll.
In preferred embodiments, the method includes, prior to lifting the ultrasonic horn into engagement with the back-up roll, moving the back-up roll to the sag distance of the ultrasonic horn about 0.015 inch such that upon the horn being lifted into engagement with the back-up roll, substantially all sag is removed from the ultrasonic horn. Thus, weight load of the ultrasonic horn is substantially dissipated for the O-rings closest to the face of the ultrasonic horn.
In preferred embodiments, the method includes bringing the anvil roll and the ultrasonic horn together primarily by lifting the anvil roll, thereby to bring the anvil roll into engaging relationship with an outer surface of the ultrasonic horn.
In some embodiments, the method includes pivoting the anvil roll about an axis perpendicular to the first axis thereby to bring the first axis into alignment with the second axis, and accordingly to bring the working surface of the anvil roll into a parallel relationship with the outer bonding surface of the ultrasonic horn.
Preferred methods include limiting downward movement of the anvil loading assembly and thereby preventing disengagement of drive gears which transmit drive power between the anvil support apparatus and the horn support apparatus.
The method preferably includes controlling the height of the back-up roll and thereby controlling height of the ultrasonic horn, by adjusting the height of the cradle arm connected to the back-up roll with e.g. an adjusting screw.
In repeated use of the bonding system of the invention, the method includes releasing the support rolls and the back-up roll from engagement with the ultrasonic horn e.g. at the end of a bonding project, and re-engaging the support rolls and back-up roll with the ultrasonic horn at initiation of a subsequent project, and thereby returning the ultrasonic horn to the same defined location.
In a third family of embodiments, the invention comprehends a method of intermittently creating ultrasonic bonds in sequentially advancing work piece segments, wherein the work piece segments to be bonded are up to about 0.25 inch thick. The method comprises passing the work piece segments through a nip defined by a frame, anvil support apparatus, and ultrasonic horn apparatus. The anvil support apparatus defines an anvil loading assembly connected to the frame and supporting an anvil roll mounted for rotation about a first generally horizontal axis. The anvil roll comprises a first relatively smaller radius portion extending about a first portion of a circumference of the anvil roll and at least one raised bonding portion having a second relatively larger radius extending about a second portion of the circumference of the anvil roll. The horn support apparatus is connected to the frame, and supports a rotary ultrasonic horn mounted for rotation about a second generally horizontal axis. The second axis is aligned with the first axis. The method comprehends bringing the horn, mounted below the back-up roll, into engagement with the back-up roll, and bringing the anvil roll into contact with the ultrasonic horn thus defining the nip, and correspondingly developing suitable pressure in the nip to create ultrasonic bonds. The method further includes activating ultrasonic energy in the ultrasonic horn, and rotating the ultrasonic horn and anvil roll in common with movement of the work piece segments through the nip, and thereby intermittently applying pressure to the work piece segments at the raised bonding portion, and creating ultrasonic bonds in the work piece segments passing through the nip at the raised bonding portion.